The buttons and messaging are inspired by a similar program in London that started in 2005.

From CNN:

The MTA has begun issuing blue and yellow “Baby on Board” buttons as part of the agency’s Courtesy Counts campaign to encourage strap-hangers to be polite to their fellow riders. The pilot program begins on Mother’s Day and runs through Labor Day.

Not only will they hate the idea that people should give up their seats for a WOMAN (or maybe the won’t, who knows with these broads), but to admit an unborn child is a BABY?! That right there is fightin’ words.